Extension cords are used for many applications, for example, tools, household appliances, lawnmowers, and many other applications. Typically, power cords are connected by inserting a plug into a socket (or a male plug into a female plug) or connecting a power cord to another power cord. During use of the cord, tension may be applied and result in the disconnection of the cord. It would be desirable to have a convenient and effective cord lock to prevent easy disconnection of power cords during use. The invention discloses such cord locks.